Tracing of User Equipment (UE), even called Mobile Station (MS), is a procedure known and can be initiated in a Public Land Mobile Network (PLMN), which is for example initiated from the Core Network (CN), either from a Home Location Register (HLR) or directly in a Mobile Switching Centre (MSC) or in a Visitor Location Register (VLR) or in a combined MSC/VLR. The initiation is performed by triggering a ‘trace invocation’ message in a network node for an active UE. Other possibility is to set a specific flag or indication in a database of UEs for idle UEs at one point in time. This flag or indication can be read at a second point in time when the UE is entering active state and will also result in triggering a “trace invocation” message in a network node. For example, a Radio Access Network Application Part (RANAP) protocol can be used for transferring a “Trace Invoke” message between the Core Network (CN), which can be a MSC or a Serving GPRS Support Node (SGSN), and a Radio Network Controller (RNC). RANAP signaling protocol resides in a control plane of Radio network layer of Iu interface in the Universal Mobile Telecommunication System (UMTS) protocol stack. Iu interface is the interface between the RNC and the CN and is defined in the 3GPP Technical Specification (TS) 25.410 and the 3GPP TSs referenced from that specification. A Radio Network Controller (RNC) receiving a “Trace Invoke” message performs local printout about all available information related to the indicated UE as a response. Relevant information can also be sent to an Operation and Maintenance Centre (OMC) if so indicated in the trace invocation request. The information could consists of e.g. the International Mobile Subscriber Identity (IMSI), a ‘trace reference number/identification’ in order for the printout to be associated with the correct trace order, the cell currently used, target cell for handover cases, various events and messages such as assignment, handover etc. Trace is used to gather information on a UE and to report the information to a collection entity for further analysis of the data. A call trace may be initiated in the RNC, in Node B or in a Radio Base Station (RBS). Tracing is described in a number of 3GPP specifications for example in 3GPP TS 32.421 V7.2.0 (2006-09) and 3GPP TS 32.432 V7.0.0 (2005-09).
An investigation is being performed, at the moment of this application, to find a possible ways to provide homes or small areas with 3G coverage for a limited number of users using a small Radio base Station (RBS). This kind of small are a radio base stations are called Home 3G Access Points (H3GAPs), Home Access Points (HAPs), Home Node Bs (HNBs) or Femto RBSs. The term Femto RBS is used in this application and is mainly targeted for private homes and small office segments and one benefit is that there is no need for alternative access technology investments or WLAN/UMA/GAN in handsets, since any existing 3G phones will work in such an environment. Examples of given 3G standards to be used are Wideband Code Division Code Multiple Access (WCDMA), CDMA2000 and Time Division-Synchronous Code Division Multiple Access (TD-SCDMA).
The Femto RBS concept is mostly relevant for a scenario using WCDMA, but it could also be applied in other cases and technologies. For example, a similar solution might be developed for 2G technologies e.g. GSM and might also be developed for LTE (Long Term Evolution), CDMA2000 or TD-SCDMA.
The Femto RBS provides normal WCDMA coverage for end users and is connected to a Radio Network Controller (RNC) using some kind of IP based transmission. A coverage area provided is called a Femto cell to indicate that the coverage area is relatively small compared with an area of a Macro cell. One alternative for the IP based transmission is to use Fixed Broadband access (like xDSL, Cable etc.) to connect the Femto RBSs to the RNC. Another alternative would be to use Mobile Broadband access e.g. HSDPA and Enhanced Uplink or some WiMAX technologies.
FIG. 1 is a block diagram illustrating a WCDMA network including Femto RBSs working as Home 3G Access Points. The wireless communications network 1 includes a Core Network (CN) 2 connected to a Radio Network Controller, RNC 3, using a standard Iu interface. Alternatively, the RNC is a Macro RNC 11 and/or a Femto RNC 10. The RNC controls all Radio Base Stations that are connected to the RNC, e.g. Macro RBSs and Femto Radio Base Stations. Other types of RBSs like Micro RBSs and Pico RBSs are also controlled by the RNC (not shown). In the figure, the RNC 3 is connected to a Macro RBS 4 and to one 6 or more Femto RBSs 5. The interface between the Femto RBSs and the RNC is an Iub interface with extensions to carry additional information needed for a Femto RBS′ and is called Iub+ interface in the FIG. 1, and is transported using an IP network providing IP connectivity between a Femto RBS and the RNC. In some scenarios the interface could be a standard Iub interface. As this IP network may consists of unprotected and uncontrollable IP networks, security mechanisms between the RNC and the Femto RBSs are typically included. Communication between the RNC 3 and the Macro RBS 4 is IP based or IP/ATM based, and the interface is Iub. The Macro RBS 4 is working as an access point for one or more wireless User Equipment 9 (UE) within a macro cell 7. The group of Femto RBSs (H3GAPs) 5 is working as access points for UEs within Femto cells 8. The RNC 3 may also communicate with a Femto RBS 6 via the Macro RBS 4. This way the Femto RBS uses the Macro RBS as an access point for wireless user equipments into the core network. The CN 2 might also be connected to two RNCs, a Macro 10 and a Femto RNC 11, dashed lines in the figure. These RNCs 10, 11 can be implemented in the same or separate physical RNC nodes. The Macro RNC 10 controls Macro Radio Base Stations, Macro RBSs, and the Femto RNC controls Femto RBSs, H3GAPs, marked with dashed lines. The Macro RNC and the Femto RNC would exchange information concerning access points, if necessary. An OSS 12 usually performs management of access points, Macro RBSs. A H3GAP manager 13 is responsible for managing H3GAPs. A H3GAP database 14 (H3GAP DB) is used to store information related to the Femto RBSs. A Security Gateway 15 might be connected between the RNC 3 and the Femto RBS group 5. The OSS, the H3GAP manager and the H3GAP DB can be standalone nodes or parts of other nodes like the RNC 3 or the CN 2. The OSS and the H3GAP manager might also be distributed programs in a network 1. An example of a Femto RBS implementation is disclosed by patent publication WO2007040454.
A Femto RBS is installed and managed by end users in a plug-and-play manner which creates special needs for such a system and giving operators restricted information and restricted access to Femto RBSs. Performing trace procedures in a network including these plug-and-play Femto cells and controlled or uncontrolled IP networks is not specified in any of the published 3GPP specifications. Femto solution based information is not specified nor is it defined how to retrieve this information in any existing systems or documentation.